1. Field of the Invention
The invention relates to the field of production printing systems and, in particular, to purging print jobs from a print data path in a print controller through a flush job message and/or a flush path message.
2. Statement of the Problem
Production printing systems associated with data processing enterprises generally include a localized print controller within the printing system. The print controller controls the overall operation of the printing system including, for example, host interfacing, interpretation or rendering, and lower level process control or interface features of print engines of the printing system. Host interfacing may include appropriate adapters for coupling the printing system to one or more host systems that transmit print jobs to the printing system. The print jobs are generally encoded in the form of a page description language such as PostScript (PS), PCL, IPDS, etc.
In whatever form the print job may be encoded or formatted, the print controller within the printing system receives the print jobs and stores the print jobs in a job spool or some other job storage system. The print controller includes a print data path from the job storage system to one or more print engines (also referred to as an “imaging engine” or as a “marking engine”). The print data path includes components that process the print jobs. For instance, one of the components interprets or renders the received information to generate sheetside bitmaps of the print job. The sheetside bitmaps represent the image to be printed on one side of a sheet of paper.
The components in the print data path also store or buffer the sheetside bitmaps in accordance with storage capabilities of the particular architecture of a print controller. The print controller then forwards the sheetside bitmaps to the print engines. The print engines have internal queues for storing the sheetside bitmaps to be printed. A print engine pulls the sheetside bitmaps off of the queue, and performs an imaging process to mark the printable medium (e.g., a sheet of paper) with the sheetside bitmaps provided by the print controller. The print engine may comprise a laser print engine, an ink-jet print engine, or another type of imaging system that transfers each sheetside bitmap to corresponding pixels on paper.
In high-speed production printers, in order to provide the print engine with sufficient pages to maintain rated-speed printing, the print data path through the print controller needs to be able to contain a lot of print job data and to be kept as full as possible. Otherwise, delays in one component can cause the part of the print data path feeding the print engine to run empty. There may be instances during the printing process when the print data path needs to be purged of the print jobs being presently processed. For instance, if print settings are changed that affect the print jobs being processed, then the print data path may need to be purged because the data being processed, such as the sheetside bitmaps, would no longer be correct.
One solution to the problem is to stop putting new data into the print data path, and let the printing process continue to empty out the old data. This works well when the amount of data in the print data path is small. However, this solution may not be desirable if the amount of data in the print data path is large, as the print engine may run for several minutes in order to empty the print data path.
Because present solutions may not be adequate, more effective ways of purging a print data path may be desired.